A linear voltage regulator is an analog circuit capable of providing a stable output voltage from an unregulated supply to a load having specific current range. Linear voltage regulators have become an essential building block in modern electronics, as having a well-behaved supply voltage that is capable of responding to faster load transients is now a requirement for most systems.
Technical specifications for linear voltage regulators include, for example, the regulator's output voltage, which defines the nominal output voltage and the minimum and maximum output values of the regulator subject to load variations (“transient response”). Other specifications include the regulator's dropout voltage, which is the minimum difference needed between the input and output voltages for the regulator to be able to still produce a regulated output, and the regulator's maximum and minimum load current capability.
A low-dropout (LDO) voltage regulator is a particular type of voltage regulator with improved dropout voltage characteristics. Particularly, a conventional LDO voltage regulator includes: (1) a series pass device (e.g., a power Field Effect Transistor or “FET”) coupled between the LDO's unregulated input and its regulated output; and (2) a high gain error amplifier that controls the drop voltage of the pass device by comparing the output voltage with an accurate reference voltage (e.g., a bandgap reference voltage). A resistor divider may also be used to scale the output voltage to match the reference voltage and to allow regulated voltages higher than the reference.
Conventional high current LDOs usually also include a bypass capacitor to achieve transient response requirements. As a consequence, high current LDOs further require a minimum load current to guarantee stability of its control loop.
The inventors hereof have recognized that lowering the minimum load current capability requirement of high current LDOs is desirable in many scenarios. One such scenario appears in the context of battery supply systems, where battery life is dependent upon the system's current consumption. In order to save battery charge, only basic features are kept on during operation. Hence, the ratio of current load (ratio of maximum and minimum load current) tends to increase, and fast transient response is required for switching between different operation modes. However, a typical LDO presents strong loss of transient performance due to loss of bandwidth at light load conditions.
The inventors hereof have also recognized that the bypass capacitor within the LDO represents a significant bill of material cost, and therefore it would be desirable to at least reduce those costs. Generally speaking, high value capacitors (over 10 uF) are expensive because they employ special materials in their construction. However, reducing the capacitance of the bypass capacitor requires a faster regulator transient response that can overcome Printed Circuit Board (PCB), semiconductor packaging, and/or other parasitic effects. These parasitic effects play an important role in the stabilization of LDOs, particularly under high loads conditions.
To address these, and other problems with conventional LDOs, the inventors hereof have developed a voltage regulator circuit with extended minimum to maximum current ratio. In various embodiments, the systems and methods described herein provide a solution that improves the performance of the LDOs and result in a better transient performance even in the presence of significant parasitics.